As a battery becomes older, it becomes less able to hold charge. It is therefore useful to be able to determine the state-of-charge of a battery.
A known method for estimating the state of charge of a cell of a battery can be found in L. Plett, et al.: “Extended Kalmanfiltering for battery management systems of LiPB-based HEV battery packs”, Journal of Power Sources, 2004, page 252-292. Below, this article will be designated by the abbreviation “Plett 2004.”